Some cover crops die over winter; others such as cereal rye must be terminated in spring. Typically, farmers planting corn into cover crops prefer to wait about two weeks after terminating before planting, making sure the cover is completely killed and won’t compete with the corn. Most are spraying glyphosate herbicide to terminate the cover crop.

The need to terminate a week or more before planting isn’t as much of a concern if the cash crop is soybeans, says Barb Stewart, state agronomist for USDA’s Natural Resources Conservation Service in Iowa. Beans have a higher tolerance for planting into a cover crop terminated within a few days either before or after planting.

Corn is the crop to be cautious about, if planting following a cover crop. Generally, agronomists recommend terminating the cover 10 to 14 days before a field will be planted to corn. “In a late spring we may not have that luxury, depending on size of the cover crop,” she notes.

The key is managing nitrogen while the cover crop is green. You don’t want rye competing with corn for nitrogen. By the time corn spikes and emerges, if the cover hasn’t been terminated soon enough, it can compete with corn. Or if you don’t apply 30 to 40 pounds of N as starter fertilizer at corn planting, or don’t apply liquid N as a carrier for herbicide, be sure to kill the rye at least 10 to 14 days ahead of planting.

Related:Tips for managing cover crops this spring

Timing the termination
Farming near Eagle Grove, Tim Smith has planted corn and soybeans into a cereal rye cover for several years. “I usually spray my cover crop ground that’s going to corn first,” he says. “Ideally, that’s a week to 10 days before I plant. After planting corn, I spray the cover crop fields going to beans.”

One benefit of waiting to terminate the rye a few days before planting soybeans or a few days after is the rye grows taller, providing weed suppression. And produces more crop residue to build soil organic matter and for greater erosion protection. “I wouldn’t call it weed control, but the taller cereal rye does help suppress weeds,” says Smith. “I still apply herbicide.”

Last year after terminating the rye cover with glyphosate, Smith planted beans about a week later. The rye was knee-high, and weather was warm enough for it to die pretty fast. He then applied a preemergence herbicide after planting but before beans emerged. These were LibertyLink soybeans, so he could come back and apply Liberty herbicide postemergence, if and where needed.